A display device that is mounted on the head and used to view a video, that is, a head mount display (HMD) has been widely known. The head mount display includes left-eye and right-eye optical units, and is configured to control a visual sense and an auditory sense in conjunction with a headphone. The head mount display configured to completely block the outside world when mounted on the head implements increased virtual reality while viewing a video. Further, the head mount display can project different videos to the left and right eyes, and can provide a 3D image by displaying an image with parallax between the left and right eyes.
For example, a high-resolution display panel including a liquid crystal element or an organic electro-luminescence (EL) element may be used as left-eye and right-eye display units of a head mount display. Further, when an appropriate angle of view is set by an optical system and a multi-channel is reproduced by a headphone, a realistic sensation like when viewed in a movie theater can be reproduced.
In the industry, a display panel configured with a liquid crystal element, an organic EL element, or the like has been known to be likely to undergo the burn-in phenomenon in an area having a large brightness difference. When a still image such as an on screen display (OSD) screen is rendered to be superimposed on a video screen, an area having a large brightness difference occurs, and thus the burn-in phenomenon occurs in the area.
The head mount display has a limitation to the number of operation buttons mountable to a main body thereof, and thus a user operation using an OSD screen is inevitably required. Thus, even when the display panel of the above-mentioned type is used as the display device of the head mount display, significant consideration needs to be given to prevent the burn-in phenomenon from occurring when an OSD screen is displayed.
For example, an OSD screen used to display a menu includes a menu background area and a menu phrase rendered on the background area. An OSD screen is basically a still image and is likely to have a large brightness difference. For this reason, when an OSD screen is displayed for a long time, the burn-in phenomenon occurs.
A video screen is configured with various video sources such as a moving image, and thus a brightness difference between pixels changes. For this reason, the burn-in phenomenon is reduced to some extent. On the other hand, in a boundary between a menu background area and an area for displaying a menu phrase, when a large brightness difference between still pixels is continued for a long time, the burn-in phenomenon remarkably occurs. Since a menu is often displayed such that the same phrase is repeatedly displayed, the burn-in is easily observed particularly in a boundary portion between the menu background area and a menu phrase.
For example, a liquid crystal display device has been proposed that prevents an afterimage phenomenon, in a state in which display content of the entire screen can be constantly determined, by sequentially moving pixels equally dispersed among pixels configuring a display screen and causing the moved pixels to display black (for example, see Patent Document 1).
Further, an organic light-emitting display device has been proposed that suppresses the burn-in from being observed even when the same image is displayed for a long time by moving a display position of the entire panel by a predetermined distance at predetermined time intervals (for example, see Patent Document 2).
Furthermore, a video display device has been proposed that prevents the burn-in by a process of lowering brightness of an OSD display (for example, see Patent Document 3).
However, in the above-mentioned related arts, it is difficult to prevent the burn-in phenomenon, particularly, in the boundary portion between the menu background area and the menu phrase. Since a video screen on which an OSD screen is not superimposed is configured with various video sources such as a moving image, the video screen is intrinsically unlikely to undergo the burn-in phenomenon. Nevertheless, when a pixel displaying black on a video screen is inserted, a screen of the video screen becomes dark, and the image quality degrades. Further, when the display position of the entire panel is moved by a predetermined distance at predetermined time intervals, the image quality of the video screen degrades, causing complaints to manufacturers. Furthermore, when the brightness of the OSD display is lowered, the OSD screen is not easily visible.